Irrigation devices spread water on the soil. A common irrigation method employed is a sprinkler which sprays water when pressurized water is supplied to the orifice.
Frequently watering is done by sprinklers connected to a main water supply line. Water flow into the main line can be controlled manually or by automatic timers connected to water supply valves.
Both methods waste a great deal of water. Plant needs and soil conditions are extremely variable over a field or yard. Soil variations such as ph, water evaporation, ambient light, ambient temperature, and drainage rate change the amount of external irrigation required to support optimum plant growth. Different plants have a wide range watering preferences. Usually, to be certain that the few plants with the maximum water needs are adequately served, users over-water the remaining plants. Automatic timers water indiscriminately, even when it is raining.
An obvious improvement would be a valve at each sprinkler that senses soil moisture and permits watering as required by the plants at that point, for those specific conditions, regardless if the water is controlled manually or automatically.
The term sprinkler will be used in this patent to refer to all plant watering devices, including, but not limited to, sprayers, misters, drip devices, and flood gates.
The terms sufficiently moist and insufficiently moist refer to moisture preferences of the plants for optimum growth as determined by the user of this device.
There are many substances that expand and contract in proportion to the amount of moisture they encounter. Some of these include hydrogels, flax, cotton, hair, leather, nylon, wood products and their derivatives such as pulp and paper. Weihe U.S. Pat. No. 4,655,076 (1987) lists over 40 materials that are moisture responsive in this way. Hatanaka U.S. Pat. No. 4,120,813 (1978) and Urry U.S. Pat. No. 5,520,672 (1996) describes how to make various others. Some moisture responsive materials can be incorporated to make a coil or thread which conveys the moisture level through movement. The term hygrometer will be used in this patent to refer to all of these substances and devices which expand and contract with changing moisture levels.